breakroleinheritance for a folder powershell csom

I am trying to break permission inheritance for certain folders in my document library in office 365. However when $folder.BreakRoleInheritance($false) is executed I get an error:

Method invocation failed because [Microsoft.sharepoint.client.folder] does not contain a method named breakroleinheritance

my code:

function GetChildFolders($RootFolder) 
{
    if($count -ne 1){
        $folderName=$folderName+'\\'+$RootFolder.Name
    }
    $Context.Load($RootFolder)
    $Context.Load($RootFolder.Folders)

    $Context.ExecuteQuery()

    $count++

    if($folderName -eq $FolderRelativePath){                                
        $RootFolder.BreakRoleInheritance($true,$false)
        Write-host "Inheritance Broken"
        $group = $Context.web.SiteGroups[$groupAD];   
        write-host "group added"
        $collRdb = new-object Microsoft.SharePoint.Client.RoleDefinitionBindingCollection($context)

        $collRdb.Add($permission)
        Write-host "Permission added"
        $collRoleAssign = $RootFolder.Item.RoleAssignments

        $rollAssign = $collRoleAssign.Add($group, $collRdb)

        $context.ExecuteQuery()
    }

    foreach($folder in $RootFolder.Folders)
    {
        GetChildFolders $folder                       
    }
}
GetChildFolders $List.RootFolder